Variable gain low noise amplifier

ABSTRACT

The present invention is related to a variable gain low noise amplifier that optimizes input matching, gain and noise characteristics, and linearity. The variable gain low noise amplifier according to an embodiment of the present invention includes a first amplifying cell that operates in a high gain mode, a second amplifying cell that operates in a low gain mode, a selectively matching circuit, and a first short-circuit means. The variable gain low noise amplifier according to the present invention selects the best operation in each gain mode so that the circuit operated in high and low gain modes does not affect a load of another circuit.

TECHNICAL FIELD

The present invention relates to a Low Noise Amplifier (hereinafterreferred to as an “LNA”), more specifically, it is related to a variablegain LNA that is operated most suitably in input matching, gain andnoise characteristics, linearity, etc.

BACKGROUND OF THE INVENTION

A first terminal is comprised of an amplifier that generally amplifiessmall signals to large signals in wireless equipment, for example aportable phone, TV, etc. This amplifier is made to have an amplifyingoperation having low noise and high gain characteristics when the signalis very small. But linearity is demanded rather than the amplifyingoperation when the signal is relatively large. Therefore, the amplifiersatisfies more than two kinds of amplifying modes according to the inputsignal level, and it is necessary that the amplifier selects one of themin the wireless frequency receiving equipment.

As a low noise amplifier of the prior art, it is disclosed in U.S. Pat.No 6,144,254 that it is possible to switch between a low gain and highgain state.

FIG. 1 shows a circuit diagram of a low noise amplifier disclosed inU.S. Pat. No. 6,144,254.

As shown in FIG. 1, the low noise amplifier comprises a common-emitterBN1 (the first NPN transistor to operate in a high gain state),common-base BN2 (the second NPN transistor to operate in a low gainstate), third NPN transistor BN3 (the third NPN transistor for providebias current in BN2), and resistor R1.

That is, a collector of the first NPN transistor BN1 is connected to anoutput terminal Pout of an LNA, a base is connected to an input terminalPin of an LNA and the first bias input terminal Bias1, and an emitter isgrounded. The resistor R1 is connected between the first bias inputterminal Bias1 and first NPN transistor BN1.

A collector of the second NPN transistor BN2 is connected to the outputterminal Pout of the LNA, a base is connected to the second bias inputterminal Bias2, and an emitter is connected to the input terminal Pin ofLNA and a collector of the third NPN transistor BN3.

A base of BN3 is connected to the third bias input terminal Bias3, andan emitter is grounded.

Hereinafter an operation of the LNA of the prior art is described,referring to FIG. 1.

In the high gain state, the Bias1 is high, and the Bias2 and Bias3 arelow. Therefore, the first NPN transistor BN1 is activated and performsthe amplifying operation of a high gain, in the high state. Here, thesecond transistor BN2 and the third transistor BN3 are turned off.

In the low gain state, the Bias2 and Bias3 are high, and the Bias1 islow. Therefore, BN2 and BN3 are activated and perform the low gainamplifying operation, in the low gain state. Here, BN1 is turned off.

The low noise amplifier shown in FIG. 1 selects one of the statesbetween high gain and low gain, and then operates the high-gain orlow-gain amplifying operation in accordance with the size of thereceived signal. But, the circuits operated for each gain state areaffected by for the load of the other, because input terminals of theemitter-common first NPN transistor BN1 and base-common second NPNtransistor BN2 are directly connected to each other, that is the base ofBN1 is directly connected to a emitter of BN2, in the low noiseamplifier shown in FIG. 1. Namely, when the low noise amplifier operatesin a high gain state, the capacitance of an emitter terminal of BN2 actsas a load for high gain circuits. As a result, the gain, matching, andnoise characteristics of the high gain state are not good, and thecapability of the low noise amplifier is reduced. In addition, when thelow noise amplifier operates in the low gain state, the capability ofthe low gain state is reduced by the capacitance of the base terminal ofBN1 in the same way as with the high gain state. Because two modeimpedance levels of the input terminal are at substantially the samelevel, the impedances act as a load against each other.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a variable gain lownoise amplifier in which the circuits are designed to operate in thebest suited way such that each gain mode does not affect the capabilityof the best suited circuit to operate in the other gain mode.

Another object of the present invention is to provide a variable gainlow noise amplifier for which input matching, gain, noisecharacteristics, linearity, etc. can display the capability of the bestsuited circuit in different modes.

Another object of the present invention is to provide a variable gainlow noise amplifier which is operated according to the size of areceiving signal in more than two amplifying modes, and can be variedbetween the gain in low gain modes.

Another object of the present invention is to provide a variable gainlow noise amplifier whose power consumption is low.

To achieve above objects, a variable gain low noise amplifier, whichamplifies the signal applied in an input terminal and outputs to anoutput terminal, comprises a first amplifying cell, which comprises afirst terminal and second terminal connected to the output terminal,amplifies the signal applied to the first terminal to high gain, andoutputs to the second terminal in high gain mode; a second amplifyingcell that comprises a first terminal and second terminal connected tothe output terminal, amplifies the signal applied to the first terminalto low gain, and outputs to the second terminal in a low gain mode; aselectively matching circuit that comprises a first terminal connectedto the input terminal and second terminal connected to the firstterminal of the first amplifying cell, and selectively changes an inputimpedance of the first amplifying cell, a first short-circuit meansconnected between the input terminal and the first terminal of theamplifying cell, and transmits the signal applied to the input terminalto the first terminal of the second amplifying cell in the operation oflow gain mode; and wherein the selectively matching circuit changes theinput impedance such that the power transmitted to the first amplifyingcell of the signal applied to the input terminal is to be maximized inthe operation of the high gain mode, and to be minimized to essentiallyzero in the operation of the low gain mode.

The variable gain low noise amplifier of the present invention furthercomprises a short-circuit means connected between the second terminal ofthe second amplifying cell and the output terminal.

The variable gain low noise amplifier of the present invention furthercomprises a short-circuit means connected between the input terminal andthe output terminal.

The variable gain low noise amplifier of the present invention isprovided, wherein the first amplifying cell comprises first, second,third terminals, amplifying element, resistor and degenerationimpedance, and wherein the amplifying element, resistor, anddegeneration impedance control the amounts of current that flow from thefirst terminal to the second terminal in proportion to the voltageapplied to the third terminal; and a first terminal of the amplifyingelement is formed to connect to the second terminal of the firstamplifying cell, the second terminal is connected with one of terminalsof the degeneration impedance, the third terminal is connected with oneof terminals of the resistor and then formed to connect to the firstterminal of the first amplifying cell, the other terminal of theresistor is applied to the HG-bias voltage of activating the firstamplifying cell in an operation of high gain mode, the other terminal ofthe degeneration impedance is grounded, and the amplifying element isconnected to common mode of the second terminal.

The variable gain low noise amplifier of the present invention isprovided, wherein the second amplifying cell comprises a first, second,and third terminals; a first amplifying element controls the amounts ofcurrent flowing from the first terminal to the second terminal inproportion to the voltage applied to the third terminal; wherein thesecond terminal of the first amplifying element is formed to connect tothe first terminal of the second amplifying cell, and the third terminalis applied to the LG-bias voltage to activate the second amplifying cellin the low gain mode operation, and the first amplifying elementcomprises an amplifying unit connected to common mode of the thirdterminal; and the second and third amplifying elements, voltage source,and variable voltage source, control the amounts of current that flowfrom the first terminal to the second terminal in proportion to thevoltage applied to the third terminal; wherein the first terminal of thesecond amplifying element is formed to the second terminal of the secondamplifying cell, the second terminal is connected to the first terminalof the first amplifying element of the amplifying unit by connectingwith the second terminal of the third amplifying element, the thirdterminal is connected to one of the terminals of the voltage source, thefirst terminal of the third amplifying element is connected to the powersource, the third terminal is connected to the variable voltage source,and the other terminals of the voltage source and variable voltagesource are grounded.

A variable gain low noise amplifier of the present invention isprovided, wherein the matching circuit comprises a first and secondinductor, capacitor, and short-circuit means; and one of the terminalsof the first inductor is connected with the second inductor and thecapacitor, the other terminal is connected to the short-circuit means,the other terminal of the second inductor is formed of the firstterminal of the matching circuit, the other terminal of the capacitor isformed to connect to the second terminal of the matching circuit and theother terminal of the short-circuit means is grounded.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a circuit diagram of a low noise amplifier of the priorart.

FIG. 2 a shows a circuit diagram of a source-common amplifier of theprior art.

FIG. 2 b shows a circuit diagram of a gate-common amplifier of the priorart.

FIG. 3 shows a circuit diagram of a variable gain LNA according to anembodiment of the present invention.

FIG. 4 shows a circuit diagram of a variable gain LNA according toanother embodiment of the present invention.

FIG. 5 a shows a circuit diagram of a first amplifying cell according tothe present invention for the variable gain LNA shown in FIG. 3 or FIG.4.

FIG. 5 b shows a circuit diagram of a second amplifying cell accordingto the present invention for the variable gain LNA shown in FIG. 3 orFIG. 4.

FIG. 5 c shows a circuit diagram of a selectively matching circuitaccording to the present invention for the variable gain LNA shown inFIG. 3 or FIG. 4.

FIG. 6 a shows a circuit diagram of the variable gain low noiseamplifier shown in FIG. 3 using circuits shown in FIGS. 5 a, 5 b and 5c.

FIG. 6 b shows an equivalent circuit diagram of an input part of thefirst amplifying cell in order to describe the operation of selectivematching circuits in accordance with an embodiment of the presentinvention, when the variable gain low noise amplifier is operated in ahigh gain mode.

FIG. 6 c shows an equivalent circuit diagram of the input part of thefirst amplifying cell in order to describe the operation of selectivematching circuit in accordance with an embodiment of the presentinvention, when the variable gain low noise amplifier is operated in alow gain mode.

DETAILED DESCRIPTION

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the attached drawings.

Here, a common source and gate low noise amplifier of the prior art willbe described, and then proper embodiments of a variable gain low noiseamplifier according to present invention will be described in detailwith reference to the attached drawings.

FIG. 2 a shows a common source amplifier of the prior art.

Referring to FIG. 2 a, a common source amplifier comprises an NMOStransistor MS21, first inductor L21, second inductor L22 and thirdinductor L23, resistor R21 and voltage source V21. The drain of the NMOStransistor MS21 is formed to connect to an output terminal Poutconnected with one of terminals of first inductor L21, the gate isconnected with the resistor R21 and third inductor L23, and the sourceis connected with one of the terminals of the second inductor L22. Theother terminal of the first inductor L21 is connected to a power sourceVDD, the other terminal of the second inductor L22 is grounded, and theother terminal of third inductor L23 is formed to connect to an inputterminal Pin of the amplifier. The voltage source V21 is connectedbetween the other terminal of the resistor R21 and the ground.

The common source amplifier shown in FIG. 2 a amplifies the signalapplied through the input terminal Pin in a high gain mode, and can bematched to the input power and noise through a degeneration of thesource. Accordingly, the source common amplifier is proper to maximizenoise characteristics and gain. But, its weak point is that linearity isbad due to a voltage amplification effect caused by capacitance of thethird inductor L23 and NMOS transistor MS21.

FIG. 2 b shows circuit diagram of gate common amplifier of the priorart.

Shown in FIG. 2 b, the gate common amplifier comprises a NMOS transistorMG21, an inductor L24, a capacitor C21, and a current source 121. Thedrain of the NMOS transistor MG21 is formed to connect to an outputterminal Pout of the amplifier connected with one of the terminals ofthe inductor L24, the gate is connected to one of the terminals of thevoltage source V22, and the source is connected to one of the terminalsof the current source 121 and capacitor C21. The other terminal of thevoltage source V22 is grounded, the other terminal of the inductor L24is connected to the power VDD, and the other terminal of the currentsource 121 is grounded. The other terminal of the capacitor C21 isformed to connect to an input terminal Pin of the amplifier.

The gate common amplifier shown in FIG. 2 b amplifies the signal appliedthrough the input terminal Pin in a low gain mode. Because it cannoteffect voltage amplification for use in an input matching circuit in thegate common amplifier, the gain and noise characteristics are badcompared with the source common amplifier shown in FIG. 2 a. But, it iseasy to match an input resistance through the gm value by controlling ofthe current that flows to the NMOS transistor because the inputresistance is 1/gm. The value of the input resistance is much smallerthan that of the source common amplifier shown in FIG. 2 a. Its strongpoint is that the gate common amplifier can obtain a very high linearitycompared to the source common amplifier, because the linearity of gm issuperior in cases in which a recently developed transistor has a smallchannel length. And it is easy for the gate common amplifier to operatea variable gain function by means of adding a circuit to vary the outputcurrent in the output terminal of the amplifier.

Hereinafter describes an embodiment of a variable gain low noiseamplifier (LNA) is described.

The variable gain LNA according to the present invention makes use of anamplification element that is a MOSFET transistor. The amplificationelement comprises a gate, source, and drain. The MOSFET transistor hasthe characteristics that allows the direction of a current flowing fromthe source to the drain or the other way to be decided according to thevalue and polarity of the voltage applied to the gate. Otheramplification elements like the MOSFET are a bipolar junction transistor(BJT), junction field effect transistor (JFET), metal oxidesemiconductor field effect transistor (MOSFET), metal semiconductorfield effect transistor (MESFET), etc.

Hereinafter describes mostly the MOSFET among the above amplificationelements. But the sprit and scope of the present invention is notlimited to the MOSFET element and may be applied all the otherequivalent elements. And hereinafter describes mostly an N type MOSFET,but it is obvious to those skilled in the art that the spirit and scopeof the present invention may be applied to a P type MOSFET and is notlimited to the N type MOSFET.

FIG. 3 shows a circuit diagram of a variable gain LNA according to anembodiment of the present invention.

As shown in FIG. 3, the variable gain LNA according to an embodiment ofthe present invention comprises a first amplifying cell 3100, secondamplifying cell 3300, selectively matching circuit 3500, and first meansof short circuit or switch SW1. The first amplifying cell 3100 comprisesa first terminal 301 and second terminal 303, and amplifies a signalapplied to the first terminal 301 for high gain while minimizingadditional noise in the high gain mode. The second amplifying cell 3300comprises a first terminal 305 and second terminal 307, and amplifies asignal applied to the first terminal 305 to control the gain in the lowgain mode. The selectively matching circuit 3500 comprises a first andsecond terminal 309, 311 and selectively changes an input impedance ofthe first amplifying cell 3100 for that the circuit operated in eachgain mode does not act on a load respectively.

Hereinafter the connections of the LNA of FIG. 3 are described.

The first terminal 301 of the first amplifying cell 3100 is connected tothe second terminal 311 of the selectively matching circuit 3500, andthe second terminal 303 is connected to the second terminal 307 of thesecond amplifying cell 3300 and formed to an output terminal Pout of theLNA. The first terminal 305 of the second amplifying cell 3300 isconnected to the first short-circuit means or switch SW1. The firstterminal 309 of the selectively matching circuit 3500 is connected tothe other terminal of the first short-circuit means or switch SW1 andformed to connect to an input terminal Pin of the LNA.

As shown in FIG. 3, the third short-circuit terminal may be comprisedbetween the second terminal 307 of the second amplifying cell 3300 andthe output terminal Pout in the variable gain LNA according to anembodiment of the present invention. And with that structure, the outputsignal of the second amplifying cell 3300 outputs to the output terminalof the LNA due to the third short-circuit means or switch SW3 in the lowgain mode operation.

Hereinafter an operation of the variable gain LNA according to anembodiment of the present invention will be described.

The variable gain LNA operates in two modes, a high gain mode and a lowgain mode according to the power level of a received signal. That is, itoperates in the high gain mode when the power level of the receivedsignal is under a threshold of power that has been decided beforehand,and operates in the low gain mode when the power level of the receivedsignal exceeds the threshold power.

The short-circuit means may reduce the signal due to having a resistancevalue in the state of short-circuit that can be disregarded, and mayoperate with a load having a finite reactance value in the open-circuitstate when it is operated in the high gain mode. Accordingly, use of theshort-circuit means in the circuit operated in high gain mode must berestrained, and the above load characteristics of the short-circuitmeans must be carefully and respectively considered for eachamplification circuit operation.

When it using the high gain mode, the first amplification cell 3100 isactivated when the first short-circuit means SW1 is opened and HG-biasis applied to the first amplifying cell 3100. And the second amplifyingcell 3300 is inert by not applying an LG-bias.

Accordingly, when it is operated in the high gain mode, the impedance ofthe second amplifying cell 3300 operated in the low gain mode does notaffect the first amplifying cell 3100 operated in the high gain mode bythe opening of the first short-circuit means SW1, and only the openimpedance of the first short-circuit means affects the high gain modecircuit. But, the input of the first amplifying cell 3100 operated inthe high gain mode is generally matched to 50˜70 ohm, that is standardresistance. due to the selectively matching circuit 3500, the openimpedance of the first short-circuit means SW1 has a high value of morethan 50˜70 ohm. So, the effect of the open impedance having a load forthe first amplifying cell 3100 is ignored. Accordingly, the variablegain LNA according to an embodiment of the present invention may be themost suitable operation in high gain mode, and amplifies the inputsignal for a high gain.

When in the low gain mode, the second amplifying cell 3300 is activatedby the first short-circuit means being shorted and LG-bias applied. And,the first amplifying cell 3100 is inert by not applying the HG-bias. Theselectively matching circuit 3500 changes the input impedance of thefirst amplifying cell 3100 in the low gain mode to a high impedance ofmore than the aforementioned decided value (generally standardresistance value: 50˜75 ohm). Accordingly, in the low gain mode thevariable gain LNA may be the most suitable operation because the firstamplifying cell 3100 is not operated to bear a load of the secondamplifying cell 3300 in the low gain mode.

FIG. 4 shows a circuit diagram of a variable gain LNA according toanother embodiment of the present invention.

The embodiment shown in FIG. 4 is different from the variable gain LNAaccording to the embodiment shown in FIG. 3 in the point that a fourthshort-circuit means or switch SW4 is arranged between the input terminalPin and the output terminal Pout. The variable gain LNA according toanother embodiment of the present invention directly transmits thereceived signal to the output terminal Pout through the fourthshort-circuit means. So, power consumption may be reduced according tothis embodiment. Moreover high linearity is provided and signaldistortion is reduced by eliminating an input signal level of post part(normally mixer) of the variable gain LNA.

FIG. 5 a shows a circuit diagram of a first amplifying cell according toan embodiment of the present invention in the variable gain LNA shown inFIG. 3 and FIG. 4.

As shown in FIG. 5 a, the first amplifying cell 3100 is embodied in acommon-source, and comprises an amplifying element MS51, degenerationimpedance DI51, and resistor R51. The drain of the amplifying elementMS51 is formed to connect to the second terminal 303 of the firstamplifying cell 3100, the gate is connected to the terminal of theresistor R51 and is formed to connect to the first terminal 301 of thefirst amplifying cell 3100, and the source is connected to a terminal ofdegeneration impedance DI51. In the other terminal of the resistor R51,when operating in the high gain mode, the first amplifying cell 3100 isactivated by HG-biasing voltage, and the other terminal of degenerationimpedance DI51 is grounded. Degeneration impedance DI51 can be made touse the passive or the active elements of resistor and inductor, etc.

As mentioned above, the common-source amplifier has excellent noise andgain characteristics, and can get satisfying input power and noisematching results at the same time, through the degeneration impedanceDI51 connected to the source of the amplifying element MS51. Also, asshown in FIG. 3, the common-source amplifier can display the capabilityof the best suited circuit for the noise and gain sides because thematching circuit 3500 is connected to the first terminal of the firstamplifying cell 3100. Therefore, when the low noise amplifier is usedwith the above common-source amplifier in the high gain mode which needsa high gain amplifying operation, it can display its utmostcapabilities.

FIG. 5 b is a circuit diagram for showing the inside structure of thesecond amplifying cell 3300 in accordance with an embodiment of thepresent invention in the variable gain low noise amplifier shown in FIG.3 or FIG. 4.

As shown in FIG. 5 b, the second amplifying cell 3300 is embodied in acommon-gate, and comprises an amplifying part 510 and gain part 530.

The amplifying part 510 of the second amplifying cell 3300 comprises thefirst amplifying element MG51. The drain of the first amplifying elementMG51 is connected to the connecting point of the source of the secondand third amplifying element MG52, MG53 of the variable gain part, andwhen operating in the low gain mode, LG-biasing voltage that activatesthe second amplifying cell 3300 is driven, and the source is formed atthe first terminal 305 of the second amplifying cell 3300.

In a variable gain low noise amplifier in accordance with an embodimentof the present invention, preferably, the current source (not shown,please refer to FIG. 2) is provided between the source of the firstamplifying element MG51 and ground. In this case, it can changetrans-conductance (gm) data of the first amplifying element MG51, and itcan control input impedance data of the amplifying part 510, by controlof the current source data.

A variable gain part 530 comprises the second and the third amplifyingelements MG52, MG53 and voltage source V51 and variable voltage sourceV52. The drain of the second amplifying element MG52 is formed toconnect to the second terminal 307 of the second amplifying cell 3300,and gate is connected to one terminal of the voltage source V51, and thesource is connected to the third amplifying element MG53. The drain ofthe third amplifying element MG53 is connected to the power source VDD,the gate is connected to the variable voltage source V52. The drain ofthe third amplifying element MG53 is connected to the power source VDD,and gate is connected to variable voltage source V52.

An amplifying part 510 comprises the first amplifying element MG51connected to a common-gate, and amplifies the signal driven in the firstterminal 305 of the second amplifying cell 3300. As mentioned above, thecommon-gate amplifier can easily controlled input matching, and it hasexcellent linearity.

As the variable gain part 530 controls the current quantities whichdivide the current coming from the amplifying part into the second andthe third amplifying elements MG52, MG53, by the control of the variablevoltage source V52, the variable gain part 530 can vary the outputcoming from the second terminal 307 of the second amplifying cell 3300,and it can control in succession the gain data of the second amplifyingcell 3300. In addition, because the current of the first amplifyingelement MG51 is not changed by the variable gain part 530, thetrans-conductance data of the first amplifying element MG51 is regular,the input matching of the second amplifying cell 3300 is not changed.

Therefore, if the variable gain part is used in the second amplifyingcell 3300, which has common-gate construction shown in FIG. 5 b, in thelow gain mode, it can perform successive variable gain functions withoutchanging the characteristic of the input matching, and a low noiseamplifier can be provided with excellent linearity.

FIG. 5 c is a circuit diagram for showing a selective matching circuit3500 in accordance with an embodiment of the present invention for thevariable gain low noise amplifier shown in FIG. 3 or FIG. 4.

As shown in FIG. 5 c, the selective matching circuit 3500 in accordancewith an embodiment of the present invention comprises the first and thesecond inductors L51, L52 and capacitor C51 and the second shortcircuit-means or switch SW2.

One of the terminals of the first inductor L51 is connected to thesecond inductor L52 and capacitor C51, the other terminal is connectedto one of the terminals of the second short circuit-means SW2. The otherterminal of the second inductor L52 is formed to connect to the firstterminal 309 of the selective matching circuit 3500, the other terminalof the capacitor C51 is formed to connect to the second terminal 311 ofthe selective matching circuit 3500, the other terminal of the secondshort circuit-means SW2 is grounded.

In the selective matching circuit 3500 in accordance with an embodimentof the present invention, the second short circuit-means SW2 can displaythe capability of the best suited circuit in a state in which the firstamplifying cell 3300 is activated by high gain mode driven HG-biasing;in case of low gain mode, i.e., HG-biasing is not driven, the selectivematching circuit 3500 is selected to have an input impedance of the highgain mode circuit block which is made by selective matching circuit 3500and the first amplifying cell 3100, in case the first amplifying cell3100 is not activated.

FIG. 6 a shows a circuit diagram of the variable gain low noiseamplifier shown in FIG. 3 using circuits shown in FIGS. 5 a, 5 b, and 5c.

As shown in FIG. 6 a, a variable gain low noise amplifier in accordancewith an embodiment of the present invention comprises the first andsecond amplifying cells 3100, 3300, the selective matching circuit 3500,and the first short circuit-means or switch SW1.

The first amplifying cell 3100 is embodied in the form of acommon-source and is operated in the high gain mode, and the secondamplifying cell 3300 is embodied in the form of a common-gate and isoperated in the low gain mode. Moreover, the selective matching circuit3500 comprises the second short circuit-means, and in high gain mode,the input of the first amplifying cell 3100 is matched by the selectivematching circuit 3500 in order that the first amplifying cell 3100 candisplay the capability of the best suited circuit; and in the low gainmode, the input impedance of the first amplifying cell 3100 is changedto a high data mode by the selective matching circuit 3500, and thefirst amplifying cell 3100 is not operated using the load of the secondamplifying cell 3300. Therefore, the variable gain low noise amplifierin accordance with an embodiment of the present invention can displaythe capability of the best suited circuit in each gain mode.

Also, a variable gain low noise amplifier in accordance with anembodiment of the present invention uses with a common-source the firstamplifying cell 3100 in the high gain mode that demands high noise andgain characteristics, and uses a common-gate with the second amplifyingcell 3100 in the low gain mode that demands high linearity andsuccessive variable gain, as a consequence of that, linearity is good,input matching is easy, and the amplifier can have a variable gain lownoise amplifier with possible successive variable gain functions.

Furthermore, in case the power level of the receiving signal is enoughlarge and amplifying is not needed because the receiving signal isdirectly passed to the output terminal by the fourth short circuit-meansor switch SW4 shown in FIG. 4, power consumption that is demanded forthe amplifying operation is not needed.

FIG. 6 b and FIG. 6 c are circuit diagrams shown in equivalent inputparts of the first amplifying cell 3100 in order to describe morespecifically the operation of the selective matching circuit 3500 inaccordance with an embodiment of the present invention in the case avariable gain low noise amplifier is operated in the high gain mode orthe low gain mode.

In the high gain mode, the second short circuit-means is open, and theinput activating the first amplifying cell 3100 can be shown in aequivalent ZHG, on. At this time, the variable gain low noise amplifiercan be gotten the capability of the best suited circuit by matching theinput impedance of the first amplifying cell 3100 by using the secondinductor L52 and capacitor C51. That is, because the electric powers ofthe variable gain low noise amplifier and the first amplifying cell3100, the high gain mode characteristic of the best suited circuit canbe realized.

In the low gain mode, the second short circuit-means is short andinactivating the input of the first amplifying cell 3100 can be shown ina equivalent ZLG, off. Here, ZLG, off as shown in the views is verydifferent from the ZHG, on data, in this case, the matching circuit 3500comprises the first and the second inductor L51, L52 and capacitor C51.The first inductor L51 handles inductance data that are sent to theinput part of the first amplifying cell 3100 providing substantialinfinite input impedance from the node 309. As it does in the low gainmode, the input part of the first amplifying cell 3100 is not affectedby in the second amplifying cell 3300. Therefore, the input of thevariable gain low noise amplifier is matched to the most suitable ofinput of the second amplifying cell 3300, because the maximum power Pinis transferred, and at the same time, the power of the first amplifyingcell 3100 is substantially zero, thus, variable gain low noise amplifierrealizes the low gain mode characteristics of the best suited circuit.

INDUSTRIAL APPLICABILITY

In a low noise amplifier in accordance with the present invention,because the operating circuits in each gain mode is not affected by theperformance of the operating circuit of the best suited circuit of theother gain mode, the each circuit can display the capability best suitedto each mode.

Also, input matching, gain, noise characteristic and linearity etc, candisplay the capability best suited to each other in different gainmodes.

Further, each circuit operates in a gain mode with at least twoaccording to the size of the receiving signals, and can vary gain in thelow gain mode.

Furthermore, because the output of each circuit can equal the receivingsignals by the short circuit-means, amplifying operation is not needed,and the power consumption is reduced.

1. A variable gain low noise amplifier comprising: a first amplifyingcell including a first terminal and second terminal being connected toan output terminal, said first amplifying cell being configured toamplify a signal from an input terminal being input to said firstterminal and output to said second terminal in a high gain mode; asecond amplifying cell including a first terminal and second terminalbeing connected to said output terminal, said second amplifying cellbeing configured to amplify said signal being input to said firstterminal of said second amplifying cell and output to said secondterminal of said second amplifying cell in a low gain mode; aselectively matching circuit including a first terminal being connectedto said input terminal and a second terminal being connected to saidfirst terminal of said first amplifying cell, said selectively matchingcircuit being configured to change selectively an input impedance ofsaid first amplifying cell, said selectively matching circuit beingconfigured to change said input impedance to maximize a power of saidsignal in said high gain mode, and to minimize said power of said signalin said low gain mode; a first switch being connected to said inputterminal and said first terminal of said second amplifying cell, saidfirst switch being configured to transmit said signal applied to saidinput terminal to said first terminal of said second amplifying cell insaid low gain mode; and a second switch connecting said input terminaland said output terminal.
 2. A variable gain low noise amplifieraccording to claim 1, further comprising a third switch connectedbetween said second terminal of said second amplifying cell and saidoutput terminal.
 3. A variable gain low noise comprising: a firstamplifying cell including a first terminal and second terminal beingconnected to an output terminal, said first amplifying cell beingconfigured to amplify a signal from an input terminal being input tosaid first terminal and output to said second terminal in a high gainmode, said first amplifying cell comprises including first, second, andthird terminals, an amplifying element, a resistor, and a degenerationimpedance; a second amplifying cell including a first terminal andsecond terminal being connected to said output terminal, said secondamplifying cell being configured to amplify said signal being, input tosaid first terminal of said second amplifying cell and output to saidsecond terminal of said second amplifying cell in a low gain mode; aselectively matching circuit including a first terminal being connectedto said input terminal and a second terminal being connected to saidfirst terminal of said first amplifying cell, said selectively matchingcircuit being configured to change selectively an input impedance ofsaid first amplifying cell, said selectively matching circuit beingconfigured to change said input impedance to maximize a power of saidsignal in said high gain mode, and to minimize said power of said signalin said low rain mode; a first switch being connected to said inputterminal and said first terminal of said second amplifying cell, saidfirst switch being configured to transmit said signal applied to saidinput terminal to said first terminal of said second amplifying cell insaid low gain mode; and a second switch being connected between saidinput terminal and said output terminal.
 4. A variable gain low noiseamplifier comprising: a first amplifying cell including a first terminaland second terminal being connected to an output terminal, said firstamplifying cell being configured to amplify a signal from an inputterminal being input to said first terminal and output to said secondterminal in a high gain mode; a second amplifying cell including a firstterminal and second terminal being connected to said output terminal,said second amplifying cell being configured to amplify said signalbeing input to said first terminal of said second amplifying cell andoutput to said second terminal of said second amplifying cell in a lowgain mode, said second amplifying cell including first, second, andthird terminals, and a first amplifying element being configured tocontrol an amount of current flowing from said first terminal of saidsecond amplifying cell to said second terminal of said second amplifyingcell in proportion to voltage applied to said third terminal of saidsecond amplifying cell, second and third amplifying elements, a voltagesource, and a variable voltage source being configured to control anamount of current flowing from said first terminal to said secondterminal in proportion to the voltage applied to said third terminal; aselectively matching circuit including a first terminal being connectedto said input terminal and a second terminal being connected to saidfirst terminal of said first amplifying cell, said selectively matchingcircuit being configured to change selectively an input impedance ofsaid first amplifying cell, said selectively matching circuit beingconfigured to change said input impedance to maximize a power of saidsignal in said high gain mode, and to minimize said power of said signalin said low gain mode; a first switch being connected to said inputterminal and said first terminal of said second amplifying cell, saidfirst switch being configured to transmit said signal applied to saidinput terminal to said first terminal of said second amplifying cell insaid low gain mode; and a second switch being connected between saidinput terminal and said output terminal.
 5. A variable gain low noiseamplifier comprising: a first amplifying cell including a first terminaland second terminal being connected to an output terminal, said firstamplifying cell being configured to amplify a signal from an inputterminal being input to said first terminal and output to said secondterminal in a high gain mode; a second amplifying cell including a firstterminal and second terminal being connected to said output terminal,said second amplifying cell being configured to amplify said signalbeing input to said first terminal of said second amplifying cell andoutput to said second terminal of said second amplifying cell in a lowgain mode; a selectively matching circuit including a first terminalbeing connected to said input terminal and a second terminal beingconnected to said first terminal of said first amplifying cell, saidselectively matching circuit being configured to change selectively aninput impedance of said first amplifying cell, said selectively matchingcircuit being configured to change said input impedance to maximize apower of said signal in said high gain mode, and to minimize said powerof said signal in said low gain mode, said selectively matching circuitincludes first and second inductors, a capacitor, and a switch, and oneterminal of said first inductor being connected to said second inductorand said capacitor, another terminal being connected to said switch ofsaid selectively matching circuit, another terminal of said secondinductor being formed to be a first terminal of said matching circuit,another terminal of said capacitor being formed to be a second terminalof said matching circuit, and another terminal of said short-circuitmeans being grounded; a first switch being connected to said inputterminal and said first terminal of said second amplifying cell, saidfirst switch being configured to transmit said signal applied to saidinput terminal to said first terminal of said second amplifying cell insaid low gain mode; and a second switch being connected between saidinput terminal and said output terminal.
 6. The variable gain low noiseamplifier according to claim 3, wherein said amplifying element,resistor, and degeneration impedance control an amount of currentflowing from said first terminal to said second terminal in proportionto a voltage applied to said third terminal, and a first terminal ofsaid amplifying element is formed to connect to said second terminal ofsaid first amplifying cell, said second terminal is connected to oneterminal of said degeneration impedance, said third terminal isconnected to one terminal of said resistor and to said first terminal ofsaid first amplifying cell, another terminal of said resistor is appliedto HG-bias voltage to activate said first amplifying cell in said highgain mode, another terminal of said degeneration impedance is grounded,and said amplifying element is connected to a common node of said secondterminal.
 7. The variable gain low noise amplifier according to claim 4,wherein said second terminal of said first amplifying element is formedto connect to said first terminal of said second amplifying cell, andsaid third terminal of said first amplifying element is applied to theLG-bias voltage to activate said second amplifying cell in said low gainmode, and said first amplifying element includes an amplifying unitconnected to common node of said third terminal of said first amplifyingelement.
 8. The variable gain low noise amplifier according to claim 7,wherein said first terminal of said second amplifying element is formedto connect to said second terminal of said second amplifying cell, saidsecond terminal of said second amplifying element is connected to saidfirst terminal of said first amplifying element by connecting to saidsecond terminal of said third amplifying element, said third terminal ofsaid second amplifying element is connected with one terminal of saidvoltage source, said first terminal of said third amplifying element isconnected to a power source, said third terminal of said thirdamplifying element is connected to said variable voltage source, and theother terminals of said voltage source and variable voltage source aregrounded.